Coated panel and method of making the same



March 21, 1961 T. w. PERKINS COATED PANEL AND METHOD OF MAKING THE SAMEFiled D90. 29. 1958 INVENTOR.

THEROLD W- PERKINS HIS ATTO NEY United States Patent COATED PANEL ANDMETHOD OF MAKING THE SAME Filed Dec. 29, 1958, Ser. No. 783,430

2 Claims. (Cl. 154-116) This invention relates to sheet metal panelsprovided with a plastic coating, andhas as its general object theprovision of an improved panel of this type and an effective method ofmaking such panels.

Further objects and advantages of the invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize the invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

Briefly stated, in accordance with one aspect of my invention there isprovided a method of making coated sheet metal panels which includes thesteps of placing a protective strip of formed plastic material on theedge of the panel (which in the past has proved to be diflicult to coateffectively with a coating deposited in liquid form), depositing a layerof plastic material on the surface of the panel in lapped relation withthe protective strip, and curing the plastic material so as to provide apanel having a continuous uninterrupted film bonded to both the panelsurface and the edge of the panel.

For a better understanding of this invention reference may be made tothe following description and the accompanying drawing in which:

Fig. 1 is a fragmentary perspective view, in section, of the edgeportion of a sheet metal panel to which this invention is applicable.

Fig. 2 is similar to Fig. 1 but shows the panel in an intermediate stageof the coating method disclosed herein.

Fig. 3 is similar to Fig. 1 but shows the panel of the present inventionin its completed form.

The present invention has been found to be particularly useful in themanufacture of tubs for dishwashing machines, and in the drawing thethree figures show the top edge portion of a dishwasher tub the sidesand bottoms of which are formed of sheet steel with the top edgesthereof having the flanged construction illustrated so as to provide aseat for a tub cover. However, it will be understood that thisparticular embodiment of the invention has been shown for illustrativepurposes only, and that the invention is applicable to the coating ofsheet metal panels of various shapes and sizes in which it is necessaryto protect an edge portion of the panel against corrosion and the like.

Referring to the drawing, the numeral 1 designates a sheet metal panelforming one of the side walls of a dishwasher tub, the top edge of thepanel having a reverse bend portion 2 arranged to provide a seat 3 for atub cover (not shown). An edge portion 4 of the panel is bent upwardlyfrom seat portion 3, the edge 5 of edge portion 4 being the uppermostpart of panel 1.

While the outer surface 6 of panel 1 is not subject to severe corrosion,the inner surface 7, being one of the inner surfaces of the dishwashertub, must be protected against the corrosive effects of detergents, foodacids and the like. Accordingly, coatings of a thermoplastic plasticmaterial, such as plastisol, have been used in the past to coat theentire inner surface of the dishwasher tub, and

since upper edge 5 of the panel is frequently exposed to some of thefluid circulated within the dishwasher attempts have been made tothoroughly coat this edge sure face as well. While plastisol in liquidform may be successfully and effectively sprayed on flat surfaces suchas inner surface 7, the spray coating of edge portions of the panel hasnot proved to be completely efiective, it being difiicult to make surethat a coating of proper thickness over the entire edge is alwaysachieved. As a practical matter, thin spots and gaps in the plastisolcoating 011 edge 5 sometime develop and the corrosive action whichbegins in such areas may proceed into the panel along the surface andunder the plastisol coating thereon. Such corrosion may proceed to thepoint where adhesion of the plastisol coating is destroyed, thuspermitting the coating to loosen and eventually expose the inner surfaceof the sheet metal.

In accordance with the present invention I provide a protective stripformed of a suitable plastic material and shaped so as to completelycover edge 5 of panel ll, making it unnecessary to attempt to spray coatthis portion of the panel. After the protective strip has been placed onthe edge of the panel a layer of plastic material is deposited on theinner surface of the panel in liquid form, by spraying or other suitablemeans. The plastic material is also deposited on the adjacent portion ofthe protective strip overlying the same surface so as to form acontinuous film. The entire coated panel may then be cured, by heat orother suitable means depending upon the particular plastic materialused, so as to bond the protective strip to the edge portion of thepanel and also to bond the coating applied in liquid form to the surfaceof the panel and to the adjacent portion of the protective stripin thearea in which these two coatings overlap. As shown in Fig. 3, theresulting product is provided with a protective coating, which may be ofany desired thickness, on all surfaces and edges requiring corrosionprotection.

Having generally described the method and product of my invention, oneparticular example will now be described. After the sheet metal panelillustrated in the drawing has been formed into the configuration showntherein and described above, the panel is thoroughly cleaned bysubjecting it to an alkali cleaning process followed by a zinc phosphatecoating. After these cleaning steps, the edge portion 4 of the panel iscoated with a phenolic base primer adhesive or any other suitable primeradhesive. Next, a thin coating of low viscosity plastisol isapplied toedge portion 4 to obtain good adhesion, and then a protective strip 8 ofU-shaped configuration and formed of a high resin content vinyl plasticmaterial is placed on the edge portion of the panel, as shown in Fig. 2.Preferably, protective strip 8 is then partially heat cured bysubjecting the panel to a temperature of 290 F. for a period ofapproximately 20 minutes. The inner surface 7 of panel 1 is then spraycoated with plastisol, care being taken to extend the coating 9 up overthe adjacent portion of the protective strip as shown in Fig. 3.Finally, the panel is again heat cured at 400 F. for approximately 20minutes so as to complete the curing of both the protective strip 8 andthe inner sprayed-on coating 9. Upon completion of this process, panel 1is provided with a protective plastic coating which completely coversthe edges of the panel as well as the flat surfaces thereof.

While I have shown and described a particular embodiment of myinvention, I do not desire the invention to be limited to the particularconstruction and order of the method steps disclosed, and I intend bythe appended claims to cover all modifications within the true spiritand scope of my invention.

1. A method of coating a sheet metal panel with a thermoplastic materialcomprising the steps of cleaning the panel, applying a primer coat tothe metal, securing a U-shaped protective strip of formed thermoplasticmaterial on the edge of the panel, spraying a layer of thermoplasticmaterial in liquid form onthe surface of the panel and on the adjacentportion of said protective strip overlying said surface, and finallyheating said panel so as to cure said thermoplastic material and bondsaid protective strip to said panel, said thermoplastic material beingthereby bonded to said panel and fused to the protective strip so as toform a continuous corrosion resistant coating on the surface and edgeportions of the panel.

2. The method of coating a sheet metal panel with a thermoplasticmaterial comprising the steps of cleaning the panel, applying a primercoat to the panel, coating one side and the edge of the panel with athermoplastic material by spraying a layer of thermoplastic material inliquid form on the surface of the panel and securing a U-shapedprotective strip of formed thermoplastic material around the edge of thepanel, there being a lap joint between the sprayed layer and theprotective strip, and finally heating said panel so as to cure thethermoplastic materials and bond said protective strip to said panel,said thermoplastic layer being thereby bonded to said panel and fused tothe protective strip so as to form a continuous corrosion resistantcoating on the surface and edge portion of the panel.

References Cited in the file of this patent UNITED STATES PATENTS2,696,865 Seller Dec. 14, 1954

1. A METHOD OF COATING A SHEET METAL PANEL WITH A THERMOPLASTIC MATERIALCOMPRISING THE STEPS OF CLEANING THE PANEL, APPLYING A PRIMER COAT TOTHE METAL, SECURING A U-SHAPED PROTECTIVE STRIP OF FORMED THERMOPLASTICMATERIAL ON THE EDGE OF THE PANEL, SPRAYING A LAYER OF THERMOPLASTICMATERIAL IN LIQUID FORM ON THE SURFACE OF THE PANEL AND ON THE ADJACENTPORTION OF SAID PROTECTIVE STRIP OVERLYING SAID SURFACE, AND FINALLYHEATING SAID PANEL SO AS TO CURE SAID PANEL, SAID THEREMOPLASTICMETERIAL PROTECTIVE STRIP TO SAID PANEL, SAID THERMOPLASTIC MATERIALBEING THEREBY BONDED TO SAID PANEL AND FUSED TO THE PROTTECTIVE STRIP SOAS TO FORM A CONTINUOUS CORROSION RESISTANT COATING ON THE SURFACE ANDEDGE PORTIONS OF THE PANEL.